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Full text of "The manufacture and properties of iron and steel"

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CHAPTEE  XI.
THE BASIC  OPEN-HEARTH PROCESS.
SECTION XIa.—Construction of a basic opens-hearth bottom.— The basic open-hearth process consists in treating either melted or solid pig-iron, or a mixture of pig-iron and low-carbon metal, upon a hearth of dolomite, lime, magnesite, or. other basic or passive material, and converting it into steel in the presence of a stable basic slag by the action of the flame, with or without the use of ore, and by the addition of the proper recarburizers, the operation being so conducted that the product is cast in a fluid state. •
The current belief that the lining is the dephosphorizing agent is a mistake, for the highest function of the hearth is to remain unaffected and allow the components of the charge to work out their own destiny. In practice it is never possible to construct either an acid or a basic bottom so that it is entirely passive, for a slag which is viscous with silida will slowly attack a pure sand bottom, and a cinder which is mucilaginous with lime will gradually eat into a dolomite hearth. For the construction of a permanent bottom, carbon, bauxite, lime, chromite, magnesite and dolomite have been used. Magnesite gives the best results, but is costly, and well-burned dolomitic limestone answers well enough. In some places the stone is used in its natural state, but the better plan is to roast it in a cupola and then grind and mix with tar. The roof and walls being made of silica bricks, it is necessary to have a joint 'of chromite or other passive material between the acid and the basic work; but at the intense heat of a melting furnace, and in an atmosphere charged with spray of iron oxide, almost any two substances will unite if pressed together, so that the joint which bears the superposed brickwork must be shielded from the direct action of the flame.
SEC. Xlb.—Functions of the basic additions.—Given a hearth capable of resisting the action of metal and slag, the problem of
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